DESCRIPTION: Autosomal dominant polycystic kidney disease (ADPKD) affects 1/1000 of the US population. The disease is characterized by the replacement of normal renal tissue by thousands of cysts and results in ESRD in approximately 50%. In this competitive renewal, we seek to follow-up on observations recorded during the most recent award. It is our central hypothesis that ADPKD results from decreased activity of the PC-1/PC-2 receptor/channel signaling complex below some critical threshold. We speculate that a variety of genetic, environmental and stochastic factors can combine to reduce the activity of the PC-1/PC-2 complex (and its effector pathways) to a level that can initiate a pathologic state. It is likely that the complex interactions between the various factors account for the significant clinical variability that is observed. In keeping with the original philosophy of this project, we propose to use novel genetic strategies to test this hypothesis. We seek to use a multi-disciplinary approach that utilizes expert clinical observations and human clinical samples, novel in vitro cell culture systems, and unique mouse models to address the problem. This grant has three aims. In the first, we will test the hypothesis that the nature of genetic mutations influences disease severity using in vitro and in vivo model systems. We will determine the sequence of mutant RNA molecules that correspond to DNA sequence mutations identified in a subset of individuals with interesting phenotypes and genotypes in our clinical database. Expression constructs that contain cDNAs that correspond to the mutant mRNAs will be expressed using our novel in vitro tubulogenesis cell culture systems and assayed for a variety of PC-1 related functional properties. A subset of mutations will be introduced into the mouse germline through homologous recombination using recombineering techniques and mouse Pkd1 BACs with the goal of making a set of hypomorphic alleles that can be combined in various combinations with our Pkd1 null allele. In the second aim, we will test the hypothesis that hemizygosity is sufficient for disease under some conditions. We will examine hepatic cysts, which are nearly 100% penetrant in our Pkd1 +/- mice, for acquired mutations of Pkd1. In the final aim, we will examine the effects of acquired loss of Pkd1 at various developmental and post-developmental timepoints and in a tissue-selective manner. A line of mice with an inducible null allele created by the PI's laboratory (Pkd1[cond]) will be crossed with a variety of Cre-expressing mouse lines. These studies should improve our understanding of the pathogenesis of this disease and provide new tools for testing potential therapies.